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Corn+Soybean Digest

What Corn and Soybean Growers Can Do to Reduce and Control Runoff and Leaching

Larry Reid nearly “needed a pontoon” to check his corn in 2008. Bob Pfanner had to replant corn three times. But both were fortunate in one way: They didn't lose much nitrogen (N) to runoff or leaching.

They were among many who have forgotten about fall N applications and switched to sidedressing or other spring applications. Nitrogen is expensive enough without it being washed away.

Reid has grown corn and soybeans in southeast Iowa at New London for over 50 years and is about ready to turn the operation over. In those five decades, he has rarely seen water wash away soil and its nutrients like in 2007, 2008 and into 2009.

“We had no fall fertilizing for the 2009 crop,” says Reid. “Those wet years pushed us toward sidedressing N when corn is about a foot tall. We put down liquid N at a rate of about 40 lbs./acre in the sidedressing.” That comes after a 140-lb. preplant-N application.

Pfanner farms in northeast Missouri near Hunnewell. “We didn't lose any N because we put it on in the spring,” says Pfanner. “We put down all dry fertilizer along with an N stabilizer/enhancer. It's a time-release product so I get long-term benefits through the growing season.”

Nitrogen runoff and leaching has been a consistent problem in parts of the Corn Belt for years. Nitrate and phosphorus readings are almost always present in streams and rivers and blamed for hypoxia in the Gulf of Mexico (see October 2008 Corn & Soybean Digest: Hypoxia: Fact or Fiction at

THE QUESTION IS how to make those readings acceptable.

Farmers, working with Extension and other state and national entities, are looking for better ways to conserve applied N for their crops and prevent losses. John Sawyer, Iowa State University (ISU) Extension agronomist, says preplant and sidedress applications of N are becoming more common because of concerns with wet spring conditions the past few years.

“Spring preplant- and sidedress-N applications are, on average, more efficient than fall application, but the difference varies with the type of season,” says Sawyer. “In dry-to-normal seasons the difference is small to no difference, and in wet seasons spring and sidedress are advantageous.”

He says growers have followed the advice to wait until soil temperatures are cold in the fall before applications, which helps reduce conversion to nitrate before the spring. “And growers are doing a better job of applying the correct N rate,” he says.

That is due to more growers following the recommendations of a corn N-rate calculator, online at The calculator enables growers to use the maximum economic return to N when deciding on application rates. The site has information for Indiana, Iowa, Michigan, Minnesota and Ohio; also northern, central and southern Illinois and for three different soil situations in Wisconsin.

With the calculator, growers can plug in their location, the per-bushel price for corn and the N cost and determine rates for either continuous corn or corn following soybeans. Selection of the fertilizer N form allows calculation of product cost.

Once the prices are plugged in, the calculator shows the maximum return to N, the rate of N application at the maximum return to N and a range of N rates that should provide a similar economic return. The range also allows flexibility in producer choice of an application rate.

Since subsurface water flow including that from tile lines are among the apparent causes of N infiltrating rivers and streams, some growers are using man-made wetlands as biofilters to capture and remove excess nutrients.

Shawn Richmond works for the Iowa Department of Agriculture and Land Stewardship's Division of Soil Conservation and coordinates the Iowa Conservation Reserve Enhancement Program (CREP). The Iowa CREP implements a program for farmers to use wetlands to filter drainage and remove nitrate from tile-drained watersheds in 37 north-central Iowa counties.

It's one of 40 CREP programs in 32 states administered by the USDA Farm Service Agency nationwide. “Growers voluntarily construct wetlands to remove nitrates,” says Richmond. “They are strategically located and designed to reduce surface-water contamination.”

The wetlands work, according to ISU research. Studies show that targeted wetlands have the potential to remove 40-90% of the nitrate in tile drainage from upper-lying croplands.

State and federal assistance is available to help growers establish the wetlands. Richmond says annually appropriated state funds are matched at a 4:1 rate by federal dollars provided by the Commodity Credit Corporation through the Conservation Reserve Program. USDA annual payments are paid to landowners for up to 15 years. Additionally, the state provides a one-time easement incentive to landowners to enter into a 30-year or permanent easement.

Richmond says potential CREP wetland sites are located using computer technology and remote data. Site conditions are evaluated according to program criteria prior to landowner contacts. “Drainage area above the wetland pool must be greater than 500 acres and up to about 4,000 acres maximum,” he says. Other CREP specifications include:

  • Resulting wetland must be between 0.5% and 2% of the drainage area (for example, a 1,000-acre watershed requires a 5-20-acre wetland).

  • 75% of the wetland pool is less than 3 ft. deep.

  • Wetland construction shall not negatively impact drainage rights of nearby upstream and downstream land.

Federal incentives include: up to 15 annual rental payments of 150% of the weighted average soil rental rate, 50% cost-share for eligible costs of establishing conservation practices and a 40% practice incentive payment of the eligible cost of practice installation.

State incentives include a one-time, up-front incentive payment to enter into either a 30-year or perpetual easement and 10% cost-share for construction costs.

For more on Iowa's CREP program, go to

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